Phospholipase A2 from Trypanosoma congolense: characterization and haematological properties

Phospholipase A2 was isolated from Trypanosoma congolense and purified to electrophoretic homogeneity. The enzyme appeared to exist in a dimeric form with subunit molecular weights of 16,500 and 18,000. It had a pH optimum of 6.8. Kinetic analysis with different substrates, showed that the enzyme had exceptional specificity for 1,2,dimyristoyl-sn-phosphatidylcholine and 1,2,dioleoyl-sn-phosphatidylcholine with Km values of 1.85 x 10(-3) M and 2.12 x 10(-3) M respectively. The Arrhenius plot was linear with an activation energy of 5.8 kcal mol-1. Inhibition studies with parahydroxy-mercuribenzoate and tributyl-tin-oxide were positive thus implicating a thiol group at the catalytic site of the enzyme. The enzyme was stable to heat treatment and possessed haemolytic and anticoagulating properties.